What is the best manga of true love?

Stories about true love are the saddest, aren't they? Hana no Namae, Nana and Paradise Kiss come to mind. Truly realistic love-sick stories.

One of the happiest would be Seven Days (it's shonen ai, but it's extraordinary)

but it really depends on the reader. you might find true love in Strobe Edge, Maid-sama, Dengeki Daisy and other popular manga as well.